Re: [boost] [outcome] expected<T&>, result<T&>

2017-05-26 0:29 GMT+02:00 Niall Douglas via Boost :

On 25/05/2017 18:33, Andrzej Krzemienski via Boost wrote:

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Niall, Are Boost.Outcome monads intended to work with references (at least lvalue references)?

The current code no. And I deliberately left out a static assert until feedback came from here.

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I get lots of compiler errors. But the messages ("constructor cannot be overloaded") indicate that it was just an omission and not a design decision.

I did leave my options open just in case. But more support code would be needed.

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If I try it with `outcome::expected` I also get these messages, but I also get a static assert saying that as per LWG decision T must be default constructible.

Vicente, does this mean you cannot use `std::expected` to return references?

Neither std::variant nor std::optional support references, and neither does std::expected in its current proposal.

Unless reviewers here are super keen on supporting outcome, I'll be adding a static assert forever preventing them soon.

But not providing them means that if I have function that returns a reference and signals failures by, say output function parameter: ``` T& find_smallest(std::array & array, std::error_code & err); ``` I will never be able to "modernize" it to use `outcome` or `expected`. Regards, &rzej;